update error page comparison with maintenance

Author: aorcsik

dist/error-pages.html

@@ -124,6 +124,12 @@ <h1>Error Pages Comparison</h1>
           <iframe class="scaled-iframe" src="https://app.bitrise.io/500.html" title="app.bitrise.io 500"></iframe>
         </div>
       </div>
+      <div class="iframe-card">
+        <label>app.bitrise.io/maintenance.html</label>
+        <div class="iframe-wrapper">
+          <iframe class="scaled-iframe" src="https://app.bitrise.io/maintenance.html" title="app.bitrise.io maintenance"></iframe>
+        </div>
+      </div>
     </div>
     <div class="iframe-column">
       <div class="iframe-card">